Group A + B beta-haemolytic streptococci

Question 1

What is the difference between gram +ve and _ve bacteria?

Answer 1

Gram positive bacteria have a thick peptidoglycan cell well which stains blue

Gram -ve bacteria have a thin cell peptidoglycan cell wall with an outer membrane (which gram +ve bacteria dont have) that stains red

Question 2

Streptococci and staphylococci are both gram positive cocci.
How can they be diffrentiated?
Why is this important?

Answer 2

1. On gram stain:
   Both will stain blue and have cocci.
   But streptococci tend to get into strips. Staphlyococci tend to forms clusters.
2. On catalase testing:
   Catalase converts H2O2 (hydrogen peroxide) into water and oxygen.
   Only staphylococci has catalase, so mixing staphylococci with H2O2 produces bubbles.

Important as guides antibiotic selection.

Question 3

What is the difference between group A and group B steptococci?

Answer 3

Both are beta - haemolytic (completely lyse RBCs)

Group A refers to Lancefield A antigen.

Group B refers to Lancefield B antigen

Question 4

Group A strep AKA?

Answer 4

Strep Pyogenes

Question 5

Group B strep AKA?

Answer 5

Strep agalactiae

Question 6

Strep pyogenes, AKA group A beta hemolytic strep causes which disease

Answer 6

Local invasion/ exotoxin release:
1. Pharyngitis ‘strep throat’
2. Streptococcal skin infections (folliculitis, cellulitis, impetigo, necrotising fasciitis) - note skin infections can also be caused by staph aureus
3. Scarlet fever
4. Streptococcal toxic shock syndrome

Delayed, antibody mediated:
1. Rheumatic fever
2, Glomerulonephritis

Question 7

SS of streptococcal pharyngitis

Answer 7

Red swollen tonisils and pharynx

Purulent exudate on tonsils

Fever

Swollen lymph nodes

Lasts 5 days

Question 8

SS of scarlet fever

Answer 8

Fever

Scarlet rash that begins in trunk/neck and spreads to extremities, sparing the face (although do get red cheeks)

Question 9

SS of rheumatic fever

Answer 9

Between 5-15y old

Following untreated pharyngitis, get fever, myocarditis, joint swelling, chorea, subcutaneous nodules and erythema marginatum rash

Question 10

PP of post-streptococcal glomerulonephritis

Answer 10

Occurs one week after streptococcal skin/ pharyngeal infection

Antibody/antigen complexes deposit in glomerular basement membrane and activate the coagulation cascade causing glomerular destruction

Question 11

SS of post-streptococcal glomerulonephritis

Answer 11

Fluid retention: puffy face, hypertension
Dark urine (due to blood in the urine)

Question 12

Where are group B haemolytic strepococci found?

Answer 12

Vaginally in 1/4 women
Can be acquired by baby on delivery

Question 13

Who do group B haemolytic streptococci harm and which diseases do they cause?

Answer 13

Neonates (aka under 3 months)

Meningitis
Pneumonia
Sepsis

Question 14

How does rheumatic fever cause myocarditis?

Answer 14

Antigens of group A beta-haemolytic streptococcus are similar to antigens in heart, so antibodies cause myocarditis

Repeated strep infections cause rheumatic valvular heart disease

Question 15

Which valves are damaged in rheumatic valvular heart disease?

Answer 15

Mitral valve stenosis most common (initially presents as regurgitation, then stenosis)

Aortic valve regurgitation/ stenosis

Tricuspid stenosis/ regurgitation

Question 16

What kind of arthritis does rheumatic fever cause?

Answer 16

Acute migratory poly arthritis - meaning joint pain comes on in many different sited throughout day/ night.

Question 17

What lifelong treatment is required in patients who have had myocarditis caused by rheumatic fever?

Answer 17

Lifelong prophylactic antibiotics to prevent further group A beta-haemolytic streptococci infection (so thus prevent further heart damage)

Question 18

Neonatal meningitis SS

Answer 18

No stiff neck

Non-specific: fever, vomiting, poor feeding, irritability

Question 19

Which 3 pathogens must be covered by empirical antibiotics when meningitis is suspected in neonates (before LP is done)

Answer 19

Group B beta-haemolytic streptococci

Listeria monocytogenes

Escherichia coli